| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Removing unneeded self joins |
| Date: | 2018-05-16 20:48:58 |
| Message-ID: | CAKJS1f_x+b5FF4cEpEt3ywEpTGrQrpDYqAkEHmxtMF=usRitSA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 17 May 2018 at 08:44, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> What I was advocating was an approach that varies according to the
> query cost, so we don't waste time trying to tune the heck out of OLTP
> queries, but for larger queries we might take a more considered
> approach.
That's tricky. If we do this, it should be done before Path
generation, so not much is known about the costs in those case.
Perhaps something can be done by looking at the number of relpages,
but I've no idea what that would be. Perhaps we need to see how costly
this operation is first before we try to think of ways to only apply
it conditionally?
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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